1. Field of the Invention
This invention relates to the formation of integrated circuit structures. More particularly, this invention relates to a multiple step process for depositing a conformal film of uniform thickness on stepped surfaces of an integrated circuit surface.
2. Description of the Related Art
In the formation of integrated circuit structures of ever smaller dimensions, it has become important to form vias or contact openings with high aspect (height to width) ratios. Processes and apparatus have been developed to fill such vias or contact openings by sputtering without the formation of voids (by premature deposition on the upper surfaces of the opening) using a plasma beam having very little angular distribution so that the opening fills from the bottom up. A process and apparatus for such sputter deposition may be found in copending U.S. patent application Ser. No. 08/647,184, filed May 9, 1996, abandoned and assigned to the assignee of this invention, the subject matter of which is hereby incorporated by reference.
It has also become necessary to use filler materials for such vias or contact openings which require a liner on the bottom and sidewall surfaces of the via or contact opening which either act as a nucleation layer for the filler material or as a diffusion barrier to prevent the filler material from diffusing into the sidewall of the opening.
However, it is very difficult to form a barrier layer or film of uniform thickness on stepped surfaces such as the bottom and sidewalls of high aspect ratio vias or contact openings using a sputtering process. Nevertheless, at least in some circumstances, a sputter deposition is the desired form of deposition of the particular liner material. It would, therefore, be highly desirable to provide a process wherein a material of uniform thickness could be sputtered onto stepped surfaces on an integrated circuit structure such as, for example, to form a liner or barrier layer on the bottom and sidewall surfaces of a high aspect ratio via or contact opening.